Surgical procedures that are carried out within the anterior chamber of the eye require at least one penetrating incision passing through the peripheral tissues of the eye such as the cornea and the sclera. One such procedure is the removal of a cataract by ultrasonic fragmentation and aspiration (phaco-emulsification) through a small-diameter ultrasonically-vibrated needle having a central aspiration conduit. During surgery the top of the needle is inserted through an incision just large enough to accommodate the diameter of the tip. Typically, incisions of about 3 mm or less are used. As aqueous humor is removed by aspiration through the ultrasonic needle tip and fluid leaks out of the incision, the fluid must be replaced or the anterior chamber of the eye will collapse. Other small needles may be used in ophthalmic and other surgery that do not employ ultrasonic vibration, but still aspirate the fluid in a chamber.
In order to prevent these problems, irrigating fluid is constantly supplied to the interior of the eye, either through a secondary incision in the eye or by irrigation and aspiration through an outer irrigation channel. The irrigation channel is usually formed about the exterior of the needle by adding an outer sleeve which fits clearly over the needle. Such sleeves are presently of a soft elastomeric material so that they can conform to the incision and compress at the distal end. Either radial or axial compression of the sleeve can cause blockage of irrigation flow, however, and it is essential to maintain flow under all conditions of operation. Moreover, with ultrasonically energized needles, if cooling fluid flow diminishes, frictional heat increases because it cannot be dissipated. The heat build-up is sudden and pronounced, and can cause scleral or corneal burns very quickly.
A number of designs have been developed to prevent such reduction in fluid flow. One such design uses a rigid sleeve material to prevent collapse of the sleeve during surgery (U.S. Pat. No. 4,983,160). However, this design does not promote conformity and sealing between the peripheral tissue at the incision in the eye and the outside of the sleeve. Consequently, there can be excessive leakage of fluid from the eye during surgery. Also this design loses the desired flexibility of the tip on the sleeve. In another sleeve version (U.S. Pat. No. 5,282,786) a rigid portion is added to the exterior of the sleeve. While this design prevents collapse of the sleeve it too results in a poor seal and excessive leakage from the incision. Also such a product is expensive to manufacture, requiring specially molded parts to include the rigid portion into the sleeve. In another configuration (U.S. Pat. No. 4,808,154), ridges are included on the interior of the sleeve. However, in use, the ridges, in a soft polymeric material, are insufficient to prevent collapse of the sleeve and reduction in the flow rate of fluid. As seen in U.S. Pat. No. 5,286,256, two sleeves have also been used, one of a polymeric material to seal against the incision and the second, a rigid sleeve to prevent collapse of the fluid conduit. However, such a unit is bulky, requiring a larger incision which can result in longer healing time and distortions in the refractive qualities of the eye. It also does not facilitate maintenance of distal end flexibility or permit full transverse flow through side ports near the distal end. These are often used to isolate irrigation from aspiration flows so that irrigation fluid is not immediately drawn into the aspiration tip.
It is desirable to provide a sleeve arrangement for an aspiration needle which seals adequately against the periphery of the incision in the eye to reduce fluid loss but which does not collapse under the pressure of the incision or tissue. It is also desirable that this combination be inexpensive to manufacture, compatible with existing flexible sleeve elements, and suitable for use with different-sized needles.